Class 7 Science

Heat

Radiation:

All hot bodies emit heat by the process of radiation. Radiation of heat does not require a medium. Sunlight comes to the earth because of radiation as there is no medium present between the atmosphere of the earth and the sun.

One can feel the heat of bonfire by standing around it. We get warmth from the room heater because of radiation.


Reflection and absorption of heat: When heat falls over an object some of the heat is absorbed by the body and some of the heat is reflected. The temperature of an object increases because of absorption of heat.

In conventional room heater you can see the reflector attached with it. The reflector of the room heater reflects the heat towards the person sitting or standing near the room heater.

Reflection is the cause that umbrella is used to protect from heat of the sun in summer. Dark color absorbs more heat while light color reflects most of the heat. That’s why wearing light colored clothes is preferred in summer, dark colored clothes are preferred in winter.



Dark clothes absorb more heat and keep one comfortable in winter. On the other hand, light clothes reflect most of the heat and keep one comfortable in summer.

Now-a-days many kitchen utensils come in black color, since utensils of black color absorb more heat and thus cooking becomes faster.

Woolen Cloth: Woolen clothes are used in winter season. Wool is a poor conductor of heat. In addition to it; air gets trapped in woolen fiber to further increase the poor conductivity of wool. This prevents the radiation of heat of our body to the surrounding and prevents the cold from surrounding to affect our body. Thus, wearing woolen cloth makes one comfortable in winter season.



Important Terms:

  • Temperature: The reliable measure of hotness or coldness of anything.
  • Thermometer: A device to measure the temperature.
  • Degree Celsius: Unit of measurement of temperature.
  • Clinical Thermometer: A device to measure the temperature of human body.
  • Laboratory Thermometer: Used to measure the temperature in laboratory.
  • Maximum-Minimum Thermometer: Use to measure the temperature of climate.
  • Conduction: Mode of transfer of heat in solids.
  • Convection: Mode of transfer of heat in liquids and air.
  • Radiation: Mode of transfer of heat without medium.
  • Conductor: Materials that allow the flow of heat through them.
  • Insulator: Materials that do not allow the flow of heat through them.
  • Land breeze: Breeze that flows from land surface to sea surface in summer nights.
  • Sea breeze: Breeze that flows from sea surface to water surface in summer days.